Thread: Determining mil value at different magnification??

Originally Posted by GWH

Just found this in a comment on a review of my scope on the vortex site.

"If you have a variable power scope and the calibration (cal.) for the subtensions of the reticle is say 14x on a 6.5-20 power scope you can determine the hash mark spacing at say 6.5x, 8x and 20x. by using the following formula.
Divide the cal. (14x) by the desired power, say 6.5x or 20x and then multiply the cal. subtension size by this answer. You can now make a chart for hold over or even ranging.
Here we go. 14x/20x=.7, 14x/8x=1.75 and so on. Now take the answer, say .7 for the 20x. Multiply the answer against the cal. subtension size.
If the subtension, (mil-dot) spacing is 3.6" at 14x it will be 3.6 x .7= 2.5" @20x. 3.6" x 1.75= 6.3" @8X and 3.6 x 2.1=7.56" @6.5x"

So ive just calculated that on 20x 1 mil spacing will equate to 2.5" @100yds, so 2.5 divided by 1.047 = 2.387 MOA (on 20x), so the top of the bottom post (5 mil) gives me 11.93 MOA, so say 12 moa.

Where as on 14x that same point on reticle gives me just shy of 17.5moa.

So thats what i wanted to know. I'll double check by actual shooting at the range anyway, as the 20x may not be a true 20x eh.

Thanks for the help guys.

Thats why I use the measure method I described. If you calculate (as above) that at 20x your scope should have 2.5 MOA between Mil dots, then you can measure that by setting a 2.5 MOA target (or bold vertical line) at 100m and at 20x this line should be the same as the distance between the mil dots on your scope. (I got 2.4 MOA from my calculation)

Bear in mind that this will also be affected by how close to 14x you scope really is as well. I usually start at the maximum zoom anyway as if you are slightly off on the 14x (say 14.3x or 13.7x) then this will affect your results as well.

If you are exactly 3.44 MOA at 14x I get 2.408 MOA

If your magnification was actually 14.5 then at 20x it would be 2.494 MOA

And if your magnification was 13.5 then at 20x it would be 2.32 MOA.

The extreme spread of the variation is .174 MOA so at 100m not likely to make much difference. Thats nearly two WHOLE inches at 1000 yds..(1.74 inches to be precise,)..so if that screws your day up then you will be a far far better shooter than most of us ever could hope to be....